1. Field of the Invention
The present invention relates to a color cathode-ray tube (CRT) and more particularly, to a color CRT having an expanded effective display area without increasing the size of the face panel, in which the space existing between the face panel and the shadow mask is effectively utilized by expanding the opening of the mask frame.
2. Description of the Prior Art
FIGS. 1 and 2 schematically show a part of a prior-art color CRT, in which a shadow mask assembly 101 is fixed to the inside of a face panel 105 made of glass. The panel 105 forms the front section of a vacuum envelope. A substantially rectangular phosphor screen 104 is formed on the inner surface of the panel 105.
As shown in FIGS. 1 and 2, the shadow mask assembly 101 includes a frame 103 with a rectangular opening and a rectangular shadow mask 102 fixed to the frame 103 to close the opening. The frame 103 has a main part 103b and a flange 103a formed at the rear end of the part 103b. The main part 103b extends in parallel to the central longitudinal axis of the envelope and the flange 103a is perpendicular to the axis. Four spring or elastic members 106, each of which is formed by an elongated metal piece bent to have a step-shaped cross-section, are respectively fixed by welding onto the outer surfaces of the main part 103b at its four sides.
The shadow mask 102, which is formed by a thin, rectangular metal plate, has a lot of regularly-arranged small apertures 102a for color selection. The mask 102 has a skirt section 102b formed at the periphery. The skirt section 102b is fixed to the front end of the main part 103b of the frame 103 by welding so as to fit into the rectangular opening of the frame 103. The section 102b is contacted with the inner surface of the main part 103b. 
The face panel 105 has a substantially rectangular main part and four side walls 105a connected to the periphery of the main part. Four stud pins 107 are respectively fixed to the inner surfaces of the four side walls 105a. 
The four spring members 106 fixed to the frame 103 are respectively engaged with the four stud pins 107 fixed to the face panel 105, thereby fixing the shadow mask assembly 101 to the inside of the panel 105 so that the shadow mask 102 is apart from and opposite to the phosphor screen 104. The engagement of the members 106 and the pins 107 is realized by hooking the end of each pin 107 with the hole of each spring 106.
Although not shown, an inner shield is attached to the flange 103a of the frame 103 to suppress the effect of the geomagnetism.
The prior-art color CRT described above is termed the xe2x80x9cmask-innerxe2x80x9d type, because the skirt section 102b of the shadow mask 102 is inserted into the inside of the supporting frame 103 and fixed thereto.
Color CRTs have been often used as display devices for electronic terminal equipment such as personal computers. In recent years, in this case, larger display areas (i.e., larger screen size) tend to be desired to improve the visibility without reducing the amount of displayed information. Thus, the popular screen size has been increasing from 15 inches to 17, 19, or 21 inches.
However, as the screen size becomes larger, the size, weight, power consumption, and production cost of color CRTs will increase abruptly. Therefore, it is preferred to increase the effective display area as much as possible without enlarging the glass envelope. In other words, it is desired to use the display area as efficiently as possible.
From this point of view, as shown in FIG. 2, it is found that the above-described prior-art CRT has a comparatively large space S between the supporting frame 103 and the opposing sidewalls 105a of the face panel 105. This space S is generated due to the thickness or height of the spring members 106. Therefore, if the size of the face panel 105 is not changed, the maximum size of the rectangular opening of the frame 106, which is entirely covered with the shadow mask 102, is limited by the thickness or height of the spring members 106. As a result, even if the space S remains unused, a larger shadow mask is unable to be applied to the face panel 105. This means that the effective display area of the shadow mask 102 cannot be enlarged. In other words, the trajectory of electron beams emitted from the electron gun assembly provided in the neck of the vacuum envelope is unable to be bent in a wider range with respect to the central longitudinal axis of the envelope.
The space S may be narrowed by decreasing the thickness of the frame 103 and/or the thickness or height of the spring members 106. However, this causes a disadvantage that the mechanical strength of the frame 103 and/or the members 106 is lowered, and at the same time, this is incapable of generating a satisfactory result.
Accordingly, an object of the present invention to provide a color CRT that expands the effective display area without increasing the size of a face panel.
Another object of the present invention to provide a color CRT that makes it possible to use a larger-sized shadow mask without increasing the size of a face panel.
Still another object of the present invention to provide a color CRT that increases the maximum angle of the electron-beam trajectory with respect to the central longitudinal axis of a vacuum envelope.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A color CRT according to the present invention has a feature that a frame for supporting a shadow mask has a front end section bent outwardly with respect to the remainder, thereby decreasing the gap or space between the frame and opposing sidewalls of a face panel.
In other words, the color CRT according to the present invention is comprised of a vacuum envelope having a face panel, a funnel connected to the panel, and a neck connected to the funnel. The envelope has a central longitudinal axis approximatley pernendicular to the panel. The panel has side walls formed at a periphery of its main part to extend approximately in parallel to the central longitudinal axis. Engagig pins are fixed to inner surfaces of the side walls.
A phosphor screen is formed on an inner surface of the main part of the panel.
A shadow mask assembly includes a frame with an opening and a shadow mask fixed to the frame to close the opening. The frame has a front section, a rear section, and a middle section located between the front and rear sections. The front section and the rear section extend approximately in parallel to the central longitudinal axis of the envelope. The front section is shifted outwardly with respect to the rear section. A periphery of the mask is fixed to the front section. Elastic engaging members are fixed to an outer surface of the rear section,
The assembly is fixed to the panel by engaging respectively the engaging members of the frame with the engaging pins of the panel, thereby locating the mask apart from and opposed to the phosphor screen in the envelope.
With the color CRT according to the present invention, the frame in the shadow mask assembly has the front section extending approximately in parallel to the central longitudinal axis of the envelope, the rear section extending approximately in parallel to the central longitudinal axis of the envelope, and the middle section intervening between the front and rear sections. The front section is shifted outwardly with respect to the rear section. The periphery of the mask is fixed to the front section. Thus, the assembly is fixed to the panel by engaging respectively the engaging members of the frame with the engaging pins of the panel, thereby locating the mask apart from and opposed to the phosphor screen in the envelope.
Therefore, the shadow mask can be made larger in size without increasing the size of the face panel. In other words, the color CRT according to the present invention makes it possible to use a larger-sized shadow mask without increasing the size of the face panel. This means that the effective display area is expanded and the maximum angle of the electron-beam trajectory with respect to the central longitudinal axis of the envelope is increased, even if the face panel is not enlarged.
In a preferred embodiment of the CRT according to the invention, the middle and rear sections of the frame of the shadow mask assembly are connected to each other to form a step-shaped or abrupt cross section.
In another preferred embodiment of the CRT according to the invention, the middle and rear sections of the frame of the shadow mask assembly are connected to each other to form an oblique or linearly-graded cross section.
The shadow mask may be fixed to an inner surface of the front section of the frame. In this case, the assembly is of the xe2x80x9cmask-innerxe2x80x9d type. The shadow mask may be fixed to an outer surface of the front section of the frame. In this case, the assembly is of the xe2x80x9cframe-innerxe2x80x9d type.